1. Field of the Invention
The present invention relates to a method and apparatus for electro-depositing a metal or metal alloy coating on at least one side of a metal strip by using at least one electrically polarized panel having a slit and a plurality of openings through which electrolytic liquid is ejected onto a corresponding side of the metal strip being coated.
2. Description of the Related Art
A conventional electro-deposition apparatus is described, for example, in German Patent Appln. No. 3209451, and includes an electrically polarized panel that includes a slit for emitting electrolytic liquid. The panel is typically made of a material that is insoluble in the electrolytic liquid.
The metal strip to be coated is conveyed in front of the slit which extends lengthwise in the direction along which the strip is conveyed. Typically, the panel is arranged so that the slit extends lengthwise in a vertical direction and the metal strip is conveyed in a vertical direction past the slit. A large amount of electrolytic liquid can flow through the entire slit at one time and thus completely fill the gap between the metal strip and panel before draining off to the sides of the panel.
However, due to the high pressure at which the electrolytic liquid is emitted from the slit, the center of the strip is usually forced away from the panel along the entire length of the strip. On the contrary, due to the hydraulic paradox phenomenon, the flow of the electrolytic liquid along the strip edges causes the strip to be drawn towards the panel. Due to these problems, it is difficult for the conventional apparatus to produce a uniform coating on the metal strip.
That is, because the strip is not evenly conveyed past the panel, the thickness of the coating deposited on the strip varies substantially over the width of the strip. Typically, the coating is thicker along the outside edges of the strip than along the center of the strip.